It is common for the properties of a single material to be insufficient to meet the performance requirements of a desired application. To obtain the desired performance, different materials may be brought together to form a laminate structure. Examples of such laminates include combination of a flexible material with a less flexible (e.g., structural) material or combination of a decorative material with a functional material. However, in many cases, the materials to be combined are not sufficiently compatible to provide the necessary adhesion to obtain a durable or high performance laminate structure.
In order to improve the adhesion of two disparate layers, a “tie layer” may be inserted between the layers of the laminate structure. The material used in the tie layer normally exhibits compatibility with the different layers but the material may not itself provide properties to the laminate other than adhesion. In short, the tie layer is the “glue” that binds the disparate layers of the laminate material together.
One laminate structure that has found use is one obtained by combining polyester or copolyester materials with papers, films, textiles or fabrics, where the materials combined with the polyester or copolyester materials may be either naturally or synthetically derived. Such laminates are used in varied applications because they are known to provide enhanced structural performance (e.g., impact protection, moisture barriers, sound barriers and sight barriers) and improved aesthetics. Examples of common uses for such laminates are locations where somewhat lightweight structural structures are needed, such as cruise ship and aircraft interiors, building interiors and office furnishings, such as partitions and other space dividers where a good appearance is desired along with structural support.
It is known that polyesters and copolyesters do not adhere well to polyolefin materials. As such, tie layers may be used to improve the adhesion of these materials. Commonly used tie layer materials are based on ethylene/vinyl acetate copolymers (EVA copolymers) or EVA copolymers containing copolymerized or grafted glycidyl methacrylate or maleic anhydride.
However, polyester or copolyester/polyolefin laminate structures having tie layers made from EVA-containing materials exhibit poor flammability properties because EVA is a highly flammable material. This property limits the use of EVA as a tie layer for structures where low flammability is required, such as in cruise ship and aircraft interiors and in office and building interiors. Materials for use in these locations require that building materials pass one or more flame tests such as ASTM D 635 (Burning Rate of Self-Supporting Plastics in a Horizontal Position), UL 94 (Flammability of Plastic Materials for Parts in Devices and Appliances) and ASTM E 84 (Surface Burning Characteristics of Building Materials).
In light of the above, there exists a need to obtain laminate structures made from polyester or copolyester materials having one or more polyolefin layers where such structures will exhibit improved performance in industry-standard flammability tests such as those discussed above. In accordance with this objective, the present invention provides improved polyester or copolyester/polyolefin structures using a material for the tie layer that results in improved performance in flammability tests.